1. Field of the Invention
The present invention relates to a reflective display device for displaying a screen image corresponding to an input image signal on a display panel by selectively driving an actuator element depending upon an attribute of the image signal.
2. Description of the Related Art
Cathode ray tubes (CRT), liquid crystal display devices or the like have been known as the display device.
Usual television receivers, monitors for computers or the like have also been known as the cathode ray tube. Although the cathode ray tube has a bright screen, it consumes a large amount of electric power. In the cathode ray tube, further, the depth of the display device is large as compared with the size of the screen.
In comparison with the cathode ray tube, the liquid crystal display device is small, and consumes a small amount of electric power. However, brightness of the liquid crystal display device is not good. Further, viewing angle of the crystal display device is not wide.
To display a color image on the screen in the cathode ray tube and the liquid crystal display device, it is necessary to use many picture elements (image pixels), which is three times as many as the picture elements of a black-and-white screen. Therefore, the device itself is complicated, a large amount of electric power is consumed, and thus, the cost is relatively high.
As a solution of the above problems, the applicant has proposed a novel display device (see, for example, Japanese Laid-Open Patent Publication No. 7-287176). As shown in FIG. 16, this display device includes actuator elements 400 arranged for respective picture elements. Each of the actuator elements 400 comprises a main actuator element 408 including a piezoelectric/electrostrictive layer 402 and an upper electrode 404 and a lower electrode 406 formed on upper and lower surfaces of the piezoelectric/electrostrictive layer 402 respectively, and an actuator substrate 414 including a vibrating section 410 and a fixed section 412 disposed under the main actuator element 408. The lower electrode 406 of the main actuator element 408 contacts the vibrating section 410. The main actuator element 408 is supported by the vibrating section 410.
The actuator substrate 414 is composed of ceramics in which the vibrating section 410 and the fixed section 412 are integrated into one unit. A recess 416 is formed in the actuator substrate 414 so that the vibrating section 410 is thin-walled.
A displacement-transmitting section 420 for obtaining a predetermined contact area with an optical waveguide plate 418 is connected to the upper electrode 404 of the main actuator element 408. In the illustrative display device shown in FIG. 16, the displacement-transmitting section 420 is located near the optical waveguide plate 418 in the OFF selection state or the unselection state in which the actuator element 400 stands still, while it contacts the optical waveguide plate 418 in the ON selection state at a distance of not more than the wavelength of the light.
The light 422 is introduced, for example, from a lateral end of the optical waveguide plate 418. In this arrangement, all of the light 422 is totally reflected in the optical waveguide plate 418 without being transmitted through front and back surfaces thereof by controlling the magnitude of the refractive index of the optical waveguide plate 418. In this state, a voltage signal corresponding to an attribute of an image signal is selectively applied to the actuator element 400 by the upper electrode 404 and the lower electrode 406 so that the actuator element 400 may make a variety of displacement actions in conformity with the ON selection, the OFF selection, and the unselection. Thus, the displacement-transmitting section 420 is controlled for its contact with and separation from the optical waveguide plate 418. Accordingly, the scattered light (leakage light) 424 is controlled at a predetermined portion of the optical waveguide plate 418, and a screen image corresponding to the image signal is displayed on the optical waveguide plate 418.
When a color image is displayed using the display device, light sources for the three primary colors are switched to control the light emission time for the three primary colors, while synchronizing the contact time between the optical waveguide plate and the displacement-transmitting plate with the cycle of color development. Alternatively, the contact time between the optical waveguide plate and the displacement-transmitting plate is controlled, while synchronizing the light emission time for the three primary colors with the color development cycle.
Therefore, in the display device proposed by the present applicant, it is unnecessary to use many picture elements, even if the display device is use to display the color image.
An object of the present invention is to improve the display device proposed by the present applicant and provide a reflective display device which makes it possible to simplify the arrangement for introducing the external light and/or the light from a light source, improve the luminance or brightness, improve the contrast, and improve the quality of a displayed image.
According to the present invention, a reflective display device comprises:
a display panel into which light is introduced;
a driving section disposed at the back of the display panel, the driving section including a plurality of actuator elements corresponding to a number of picture elements;
a picture element assembly provided on each of the actuator elements, the picture element assembly including at least a light-reflecting section and/or a light-absorbing section; and
a light-absorptive and/or a light-reflective substance filled between the display panel and the driving section,
wherein the actuator elements are selectively driven according to an attribute of an input image signal for controlling displacement of the picture element assembly in a direction closer to or away from the display panel, thereby adjusting degree of light-absorption and/or light reflection between the display panel and the picture element assembly so that a screen image corresponding to the image signal is displayed on the display panel. Preferably, the display panel is transparent.
Accordingly, the light from the external light or the light source is simply radiated onto the display panel, without introducing the external light or the light from the light source so that the light is totally reflected in the display panel. Therefore, it is possible to greatly simplify the arrangement for introducing the external light or the light from the light source.
Light emission is effected when a thickness of the light-absorptive substance between the display panel and the picture element assembly is decreased by displacing the picture element assembly in the direction closer to the display panel. Light emission is stopped when the thickness of the light-absorptive substance between the display panel and the picture element assembly is increased by displacing the picture element assembly in the direction away from the display panel.
Alternatively, light emission is stopped when a thickness of the light-reflective substance between the display panel and the picture element assembly is decreased by displacing the picture element assembly in the direction closer to the display panel. Light emission is effected when the thickness of the light-reflective substance between the display panel and the picture element assembly is increased by displacing the picture element assembly in the direction away from the display panel.
The picture element assembly may have a color layer. In this arrangement, the light-reflecting section and/or the light-absorbing section of the picture element assembly may serve as the color layer.
Further, for example, a three primary color filter, a complementary color filter, or a color scattering element may be used as the color layer. The xe2x80x9ccolor scattering elementxe2x80x9d herein refers to an opaque one which is obtained, for example, by dispersing a dyestuff such as a pigment in a resin or the like.
In this case, the light-absorptive substance (light-absorptive material) is not limited to black one. For example, a blue light-absorptive material may be used. In this case, for example, when it is assumed to use no color filter, it is possible to display white dots on a blue background. Further, when a red color filter is used in combination, it is possible to display red dots on a blue background.
As described above, it is possible to select arbitrary background colors and display colors by combining colors of the color filter and the light-absorptive material. Similarly, when the light-absorbing section is formed for the picture element assembly, for example, a black color can be displayed on a blue background.
As the light-absorptive material, it is possible to use a liquid, an emulsion, and a gel dispersed with a pigment or a dye, and a flexible resin material and a combination thereof. A sponge or the like impregnated with the liquid can also be used.
It is possible to use the liquid obtained by dispersing a pigment in water, oil, or organic solvent having a low vapor pressure, and a colored dye. For example, it is possible to use one obtained by dispersing carbon black in silicone oil having high electric insulation. It is preferable to select, as the silicone oil, an oil having a low viscosity in order to quickly switch the image display. The carbon black is more preferably used if it is applied with a surface coating in order to enhance the electric insulation.
As the light-reflective substance (light-reflective material), it is possible to use a liquid, an emulsion, and a gel dispersed with a pigment or a dye, and a flexible resin material and mercury and a combination thereof. A sponge or the like impregnated with the liquid can also be used.
As the method for controlling the light transmittance of the light-absorptive material or the light-reflective material, it is preferable to change the thickness of the light-absorptive material or the light-reflective material (distance between the display panel and the picture element assembly) by the displacement of the actuator element. The thickness or the displacement is, preferably, though not limited to, not less than 0.1 xcexcm and not more than 10 xcexcm.
It is also preferable that a concave/convex structure is provided for a portion of the picture element assembly facing the light-absorptive material or the light-reflective material. When the light-absorptive material and/or the light-reflective material is a fluid, the concave/convex structure forms the flow passage. Therefore, the response performance of emitting light and stopping the light emission is improved. A convex form is also preferably used.
It is also preferable to use a transparent layer at a portion of the picture element assembly facing the light-absorptive material or the light-reflective material. The transparent layer adjusts the height of the picture element assembly, for example, so as to obtain a uniform thickness of the light-absorptive material and/or the light-reflective material in the natural state of the actuator element. The concave/convex structure or the convex shape may be formed for the transparent layer.
It is possible to improve the light emission luminance and/or the contrast by radiating the light from the light source onto the display panel, making it possible to enhance the performance of visual recognition. As the gradational expression system, it is preferable to use any one of or a combination of the area gradation, the time gradation, and the voltage gradation.
According to the reflective display device of the present invention, an ultrathin type low electric power-consuming display can be constructed. Therefore, for example, the reflective display device of the present invention is effective for a large screen display constructed by arranging a plurality of display devices of the present invention vertically and laterally respectively. Such a display requires no projection space as compared with a projector, which can be installed even in a narrow space.
In addition to usual oblong displays, it is possible to form screens of various shapes. For example, it is possible to form the laterally longer screen, the vertically longer screen, and the circular screen by arbitrarily changing the number of the arranged display devices of the present invention. If the display devices of the present invention are curved, a curved display can also be formed.
The large screen display is applied to the public, for example, in waiting rooms, lobbies, and corridors of stations, hospitals, airports, libraries, department stores, hotels, and wedding halls, based on the use of the features of the thin type, the large screen, and the wide angle of visibility. Further, the large screen display may be also utilized for screens of cinema complexes, sing-along machine or karaoke boxes, and mini-theaters. The large screen display may be used in both indoor and outdoor conditions.
When the color layer is provided for the picture element assembly, then the color layer may be formed at an upper portion of the light-reflecting section of the picture element assembly, or the color layer may be formed on the front surface or the back surface of the display panel. Specifically, when a large number of reflective display devices of the present invention are arranged for a display panel or a frame (including a lattice frame) having a large size to construct a large screen display, the color layer may be formed on the front surface or the back surface of the large-sized display panel. Alternatively, for example, a plate or a film, which has the color layer, may be provided for the display panel. When the color layer is provided for the display panel, a color filter is preferably used. In this case, as the picture element assembly, it is possible to use any one of the white scattering element, the color scattering element, and the color filter as the color layer. However, it is particularly preferable to use the white scattering element.
The above and other objects, features, and advantages of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings in which a preferred embodiment of the present invention is shown by way of illustrative example.